State of biological and physiological knowledge

Venous circulation
Circulation of fluids
venous Blood, C.R.L, lymph


>> State of biological and physiological knowledge regarding the blood circulation back to the heart (venous circulation):


- Given the veins' limited number and the thinness of their smooth muscular fibers, the venomotor action when it occurs is itself very limited.

- Veins are equipped with one-way valves preventing the blood from "ebbing".

- When a vein is tied, pressure increases significantly beyond the usual norm (up to the level of arterial pressure).
- Which ever part of the venous system is explored, the pressure ensuring the blood flow is low, inferior to 15 mm Hg (pressure of the blood coming out of a capillary).

- Venous pressure observed in a laying subject.

- The pressure in the venules is the result of that in the arterioles transmitted through the alveolo-capillary system.
- In an experiment conducted on a dog given curare in order to stop the skeletal striated muscles from contracting, whose thorax has been open to stop thoracic depression and whose pulmonary ventilation is artificially aided, there will be no muscle contraction. Nevertheless, the back flow is not impaired and even continues a few seconds after the heart stops, through stimulation of the pneumogastric nerve. This is usually explained by the elasticity of the arteries, arterioles and capillaries which route the blood towards the veins.

-The intrathoracic depression is

–   7 cm H2O upon exhalation
– 14 cm H2O upon deep inhalation
– 20 cm H2O upon forced inhalation.

- Contractions of skeletal muscles are considered to help venous circulation. Great pressure between the muscle fibers compress the blood vessels emptying them. Skeletal muscle exert their pressure not only on capillaries and venules, but also on bigger veins travelling between the muscles fascicles.

- Blood pressure in the arteries perpendicularly crushes the veins emptying them. The arterial systolic expansion during the heart systole is deemed incidental.
- In a standing man, pressures reaches 90 to 120 cm d’H2O in the internal saphenous vein level with the malleolus, in spite of the valves.

·         Veins are equipped with one-way valves which prevent the blood from flowing backward ; they make up an anti-ebbing system. Classical theory has that the veins are flatten when muscles contract, thus expelling the blood towards the heart. They fill up again when the muscles relax.



Valvule fermée : closed valve.
Sang propulsé vers le cœur par compression : blood propelled towards the heart by compression.
Valve ouverte : open valve.
Veine comprimée par le muscle contracté : vein compressed by the contracted muscle.
Contraction : contraction.
Flux rétrograde refoulé par la valvule fermée : backward flow stopped by the closed valve.

Diagram 1 - Contraction of the twin muscles expels the venous blood upward, the valves act as a anti-backflow system. Diagram adapted from Moore-Dalley (4)

-      The vis à tergo phenomenon.

"Arteries and veins make up a kind of U-shaped tube in which the pressure exerted by the weight of the fluid is the same on each point of one or the other branch located on the same horizontal plane."

A high level of venous pressure in the feet is nevertheless still compatible with a normal venous circulation through the simple mechanism of the vis à tergo. Indeed near the tibial malleolus, the venous blood column exerts, solely because of gravity, a pressure of 90 cm d’H2O, if such is the difference of level between the heart and the malleolus. Actually gravity has the same effect on arteries and arterioles located on the same horizontal plane (1). Consequently, the pressure ensuring the blood flow in the capillaries always equals the pressure in arterioles minus the pressure in venules, both being increased by 90 cm d’H2O because of gravity. The vis à tergo (pressure in the venules resulting from the heart pulse) is therefore also increased by 90 cm d’H2O.

Hermann & Cier.


- Poiseuille's law

Poiseuille defines the laws of laminar flow.
In a rectilinear, cylindrical tube of constant cross-section, the flow Q is obtained through the following equation :


∆P π r4
Q =
8 L n

in which ∆P is the pressure difference between the two ends of the tube, r its radius, L its length and n the viscosity ratio of the liquid flowing in it.
On the basis of this formula, the pressure difference ∆P can be calculated when the other elements are known :

Q x 8L n
∆P =
π r4

Poiseuille's formula shows that, when a liquid flows through a rectilinear tube of constant cross-section with a constant flow-rate, the pressure difference all along the tube, between the two ends, must be linear. Indeed, if Q, n and r are constant, it follows that :

∆P = Cte x L.

Diagram 2 - Variation of the lateral pressure when a fluid flows through a rectilinear tube of constant cross-section.
Diagram adapted from Hermann & Cier

The pressure difference between the point of entry and any given point of the tube will therefore be the greater the further away from the point of entry this point is.
This can be demonstrated through a simple experiment.
A horizontal, rectilinear tube of constant cross-section starts from the infero-lateral part of a tank.
A series of vertical parallel tubes is fixed laterally to this tank. The tank is then filled with water up to a certain height H. The water flows through the horizontal tube and its level in the lateral tubes, perpendicular to the direction if the flow, gradually and steadily decreases the further it flows away from the tank. The water level H stands for the pressure at the point of entry of the system. There is no pressure at all at the other end. The vertical tubes (piezometric tubes) show that, in accordance with Poiseuille's law, the pressure drop is linear all along the system.
Poiseuille's law can not be applied to the vascular system. Even taking only into account the instants when the cardiac flow, i.e. the flow rate at the point of origin, is constant, vessels can not be regarded as rectilinear tubes of constant cross-section. Arteries sport numerous ramifications and successive bends, and their caliber progressively decreases from the aorta to the arterioles which precede the capillaries. The latter, although very abundant, are extremely tiny tubes (a few microns or dozens of microns). In the venous system ensuing from them, the evolution of the caliber is reversed, the veins getting bigger as they get nearer to the heart. Not taking the ramifications and bends into account, the vascular system can schematically be regarded as a flowing system made up of three parts : the first of large caliber, the arteries ; the second of small caliber, arterioles, capillaries and venules ; and the third of large caliber, the veins. In such a system, the pressure drop between the origin and the end is not linear, which is easily demonstrated with a piezometric diagram.

Diagram 3 - Variation of the lateral pressure when a fluid flows through a rectilinear tube with a narrowed middle segment. The dotted line represents the pressure drop as it would be along the tube if its cross section was constant.
Diagram adapted from Hermann & Cier.


The tube horizontally connected to the infero-lateral part of the tank is made up of three segments of equal length AIV, but the middle segment's radius is inferior to the two others. This narrowing represents the part of the system made up of arterioles, capillaries and venules. When the tank is filled with water up to the level H, the liquid flows through the horizontal tube, but the level of water in the piezometric tubes laterally connected to the system does not steadily decrease the further away it flows from the tank. The narrowing increases the lateral pressure upstream and decreases it downstream.

This experimental result could actually have been deducted from Poiseuille's law. In the flowing system represented in diagram 70, as long as the tank's water level is kept at a level H, the flow rate is constant and the same in each of the three segments. The pressure drop between each of their respective ends is calculated as follows :

K                                  Q 8L n
∆P =                             ( K =                             = Constant).

r4                    π

In segments A and V, the pressure drop ∆P will be very small because of the tubes' large caliber and because the value of r4, used as denominator, is high. On the other hand, in the middle segment 1, the pressure drop between the two ends will be great because the tube's radius is small. Poiseuille's law also shows that small variations in the middle segment's radius will have significant impact on ∆P. Indeed the pressure gradient is inversely proportional to the 4th power of the radius (r4). Meaning that when the latter is multiplied by 2, the pressure drop is divided by 16.
There is no doubt that the vascular system is a much more complex piping set than the diagram which has just been studied. Analyzing it is much more difficult, because the narrowed part is not limited to the middle segment's single pipe. There is between the aorta and its main forks on the one hand, and the big veins on the other hand, a number of narrow parts set in series (arteriole, capillary, venule in succession) and in parallel (same succession for each organ or distribution area of one big arterial fork). Furthermore, each of the vascular system's segments sports bends and ramifications which have the same effect as narrow parts, in that they are relative obstacles to the blood flow. Thus, successive ramifications in the arterial system add to the effect of arteriole narrowing in maintaining the pressure. Because they are large caliber vessels located upstream from narrow parts, the pressure drop ∆P in the arteries, from the aorta's point of origin to  the arterioles, will be small. On the other hand, the arterioles being vessels of small caliber sporting many ramifications and bends, the pressure gradient, between the point of entry and the point of exit leading into the capillary network, will be high.

The pressure drop will still be significant through this capillary network because of its narrowness. Nevertheless, its absolute value will be inferior to that in the arterioles for two reasons :
- The considerable number of capillaries ensures a high tissue blood flow, despite a low one in each single capillary ;
- Capillaries are shorter than arterioles. Poiseuille's law shows that, when the flow rate and the caliber don't change, the pressure gradient is proportional to the length.

Q 8 n
( ∆P =                                    x  L ) .           
π r4         

There remains the veins and the venules. The blood progresses in them under very low pressure conditions. Numerous factors make this possible, the main one being that, from the venules to the auricle, the vessels' caliber steadily increases so that the blood flow does not go through any narrowing.
This is enough for the necessary and sufficient pressure gradient ensuring the blood flow between two points in the venous system to be low. The nearer to the auricle, the lower
These theoretical observations are confirmed by measurements carried out in various points of the vascular system. In the systemic circulation, it appears, in particular, that the greatest pressure drop is observed in the arteriolar system. Diagram 71 shows this evolution : the pressure values entered below the Y axis, represent the average pressure to be found in the vascular system's segment entered below the X axis.
From a functional point of view, the arterial pressure's sole function is to ensure a sufficient blood flow to the organs in order to meet their metabolic demands. The flow rate, at any given point of the circulatory system, is the volume of blood flowing at this point during the time unit. It varies according to the linear speed of the flow and the surface of the chosen vessel's cross section (Q = v x π r2).

Gros troncs artériels : large arterial trunks
Artérioles : arterioles
Capillaires : capillaries
Grosses veines : large veins

Diagram 4 - Evolution of pressure in the whole circulation. This diagram shows, whichever part of the circulation system is considered (A, B, C, D, E, F or G), the total flow rate value is always the same.
Diagram adapted from Hermann & Cier.


Because the blood gradually spreads on a more and more large surface as it progresses along the arterial system (image of the cone), the flow speed gradually decreases from arteries to capillaries ; at this point, it reaches a minimum, to then increase again in the veins. But the flow rate in a vessel is also expressed by Poiseuille's law, according to the pressure difference between the two ends of the vessels, to its length, its radius and to the blood viscosity

∆P π r4
( Q =                            ).
8 L n


The equality of these two ways of defining the flow rate writes as follows :

∆P r2
V =
8 L n

Therefore the speed of the blood flow depends on the perfusion pressure and on the surface of vascular cross section. When the vessel's caliber does not change, the local flow rate depends on the pressure, which also governs the flow speed. In fact, the whole process is even more complex because blood is a heterogeneous liquid so its flow speed is not the same at all points of a straight vessel section, especially in a small caliber vessel. Because of parietal frictions due to contact with the vessels' walls, the progress of the blood is dramatically slowed down. It speeds up again in central areas where red cells tend to gather.
In any case, speed, pressure and flow rate are closely linked to each other. Whatever the level at which a total section of the vascular system is made, diagram 4 clearly shows that the flow rate value is the same. On this basis, the pressure value and the speed value will adapt to local conditions which are constantly modified by the action of vasomotricity."

Hermann & Cier.

>> Contradictions in the current theory.

- In the experiment on the dog given curare, when the heart stops and the arteries retract,  the blood tends to go back up rather than face the resistance of capillaries further down. If it stops only a few moments after the heart,  it may be, as will be discussed later, that the skeletal muscle pump is no longer provided with arterial blood (Arterial circulation has no anti-back flow system [valves] preventing arterial blood to go back to the heart). This experiment also demonstrates that the venous system can bring the venous blood back to the heart without the help of thoracic depression.

- In a subject struck with a peripheral type of paralysis (flaccid), the nervous conduction needed for the skeletal muscles to contract is totally lacking. Such a subject can kept standing without developing a venous stasis serious enough to stop the blood from going back to the heart. With a pressure of 2 cm H2O at the exit of the capillary and a average depression of 10 cm H2O at mediastinal level, the venous blood manages to go back to the heart despite a column of 90 à 120 cm H2O at malleolus level.
- In the vis à tergo theory, the vessels' tremendous resistance (circumference, walls, bends blood viscosity), plus the deformation of the blood cells by the capillaries must be taken into account. At the exit of the capillary, positive pressure is 1,5 cm Hg. Furthermore, the heart propels the blood with an average force of 120 mm Hg. Arterial circulation would need 120-15=105 mm Hg to bring the blood from the heart to the capillary and 15 mm Hg to bring back from the capillary to the heart, which is about 1/10 of the actual force in the arterial system.
-      Poiseuille's law applied to the vis à tergo phenomenon.

°      First of all, Poiseuille's law can not be applied to the vascular system.
°      Indeed blood and vascular walls exhibit a non linear therefore non Newtonian  behavior, particularly in the stagnation zones or in the small vessels (with a diameter inferior to 500 microns). (1)
°      Let us consider two columns, one descending artery and one ascending vein, and apply Poiseuille's law to each of them bearing in mind that « The gradient pressure is inversely proportional to the fourth power of the radius (r4). Meaning that when the radius is multiplied by 2, the pressure drop is divided by 16 ». So both columns have the same pressure :

°      Arterial column in a standing subject :
systolic pressure is 90 cm Hg + 12 cm Hg = 102 cm Hg.
°      Venous column :
1,5 cm Hg +90 cm Hg = 91,5 cm Hg.
°      If the arterial column is chosen as reference, it ensues that :
the venous pressure VP is 10 % lower than the arterial pressure AP (AP = 1, VP = 0,9).

°      Veins being on average twice as big, they will not slow the flow rate so much, hence the pressure will be divided by 16 according if we stick to Poiseuille's law.





Veines : veins
Artères : arteries
Veinules : venules
Capillaires : capillaries
Artérioles : arterioles

Diagram 5 - Veins are twice as big and twice as numerous as the arteries. In the lower limbs, the venous system volume is 8 times superior to the arterial system volume (2* πr2).

- Veins are also twice as numerous, which divides by two the vessels resistance.

In total, the venous pressure will be 0,9 x 16 x 2 = 28,8 times superior to the arterial pressure for the same volume of blood. Furthermore, another type of resistance is added when the blood goes through the capillaries, not because of their length but because of their cross section which forces the blood cells to deform. The flow speed decreases dramatically : 3 to 7 blood cell per capillary in one second. Thus the vis à tergo theory can not be considered 100 % reliable, as least as far as the venous back flow in lower and upper limbs is concerned.
- The osmotic pressure occurs between the capillary and the extra cellular environment. To what extent is this tissue environment enlarged by the 90 cm of water pressure through the lymphatic ways in which the flow is notoriously slow ?
Although the vis à tergo theory should not be entirely discarded, its usefulness must nevertheless be put into perspective.
Also, if things actually worked according to this law and fortunately they don't, the pressure, coming from the arterial column and allowing the blood to flow back through the veins, would be observed to be 120 cm H2O in the saphenes in erected state. Any break in a vein (wound) would result in a blood flow much more powerful than it actually is.
However, the vis à tergo theory seems to match the vascularization of specific organs particularly the renal glomeruli and the brain. They are both doubly remarkable because their venous system is more or less equivalent to their arterial system, in number and in volume (one artery and one vein of the same caliber), and because they sport cavities, the skull and the glomeruli, in which pressure does not vary.




Tube proximal : proximal tube
Epithelium de la capsule de Bowman : epithelium of Bowman's capsule
Espace de Bowman : Bowman's space
Podocytes : podocytes
Artériole afférente : afferent arteriole
Artériole efférente : efferent arteriole

Diagram 6 - The renal glomeruli, a cavity in which pressure is constant

Anatomy itself belies the theory of the flattening of the veins during muscle contractions. Observation shows how carefully vessels are located precisely so as to be free of such constraints. For example, the path of an important vessel, the femoral vein, is protected from muscle contraction, in front by the internal intermuscle wall and laterally by Hunter's aponeurosis.

Diagram 7

Canal fémoral : femoral canal
Arcade crurale : crural arcade
Artère : artery
Veine : vein
Cloison intermusculaire : intermuscle wall

Arteries and veins are protected from muscular contraction by intermuscle walls.

Artère fémorale : femoral artery
Veine fémorale : femoral vein
Ganglion de Cloquet : Cloquet's gland
Ligament de Gimbernat : Gimbernat's ligament
Veine saphène interne : internal saphenous vein

Diagram 8 - Level with the femoral arcade, the femoral vein is located away from the Psoas which could otherwise flatten it when contracting. They are also separated by the artery.


Nature has taken care to protect the veins from external influences. Had it been otherwise, veins would be thinner and more numerous. They would intimately merge between the various muscles fascicles, which is not the case. Furthermore, arteries are often close to the veins, they are submitted to the same conditions, yet they are not endowed with an anti-back flow system. Flow rates in venous vessels occur under low pressure and are submitted to dramatic variations :
- Variation in the height of limbs momentarily reducing the flow rate.
- Pneumatic contraction forcing the venous blood back
increase of abdominal or diaphragmatic pressure.

valves have no part in bringing the blood back to the heart. They only stop it from flowing backward.

Valvule fermée : closed valve.
Sang propulsé vers le cœur par compression : blood propelled towards the heart by compression.
Valve ouverte : open valve.
Veine comprimée par le muscle contracté : vein compressed by the contracted muscle.
Contraction : contraction.
Flux rétrograde refoulé par la valvule fermée : backward flow stopped by the closed valve.

Diagram 9 - Ejection of the venous blood induced by the contraction of the feet's muscles during walking would be prevented by the simultaneous contraction of the twins.
Diagram adapted from Moore-Dalley (4).

Regarding the theory on the flattening of the veins supposedly allowing the blood to flow back to the heart : the contraction of the twins flattening the saphena vein would stop the blood from being ejected from the muscles underneath (foot muscles contracting simultaneously, notably during walking (diag 9)). The ejection of the blood during muscle contraction is known to be particularly effective. Why then prevent it ?


>> Osteopathic theory on fascias.


- Cranial mechanism

Skull, spine, sacrum and coccyx are driven by a force producing inhaling and exhaling movements. To osteopaths, the drive of these mechanisms is the  production de C.R.L. from the choroid plexus (2 7cm long and 0,5 cm wide tubes).

Ventricules : ventricles
Plexus choroïde : choroid plexus

Diagram 10 - C.R.L production in the choroid plexus is synchronized with the cardiac systole.
Diagram adapted from Vander-Sherman (3).

Cranial rhythms vary from 6 to 15 breathing cycles per minute, the normal average being 12 cycles per minute. C.R.L. is produced in the choroid plexus which line the interior of the ventricular cavities of the two lateral ventricles. It goes through the third ventricle through the holes of Monro, then on to the fourth ventricle by way of the aqueduct of Sylvius as well as of the anterior side towards the preprotuberantial cistern, and from the fourth ventricle to the vertebral canal through the canal of the ependyma.





Ventricules : ventricles
Moelle épinière : spinal cord
Dure-mère-arachnoîde : arachnoid dura mater
Espace sous arachnoîdien : subarachnoid space
Pie-Mère : Pia-Mater

Diagram 11 - C.R.L. circulation in the ventricles
Diagram adapted from Vander-Sherman (3)

From the cerebral trunk,  the C.R.L. travels through small openings towards the sub-arachnoidian space where it reaches the surface of the encephalon and of the spinal cord. The C.R.L. goes back to the venous system by way of the arachnoidian villosities and mainly ends in the longitudinal venous sinus.
The C.R.L. may travel further through the peripheral nerve by way of the «tubular canals» to reach the extracellular space at the end of it (nervous ends, motor endplate, etc.)(C.R.L. markers found in the limbs' extremities). This production and resorption of C.R.L. brings about movements of flexion and extension in the set of cranial bones mainly revolving around the sphenobasilar axis. These movements are transmitted through the duremerien manchon to the sacrum which will be mobilized between the two iliac bones.



THE PART OF CORPORAL FASCIA

"The corporal fascia is like a lamellar sleeve of slightly mobile conjonctive tissue, running continuously from head to foot. Between these parallel strips are pockets containing the visceral and somatic structures of the human body.

Bearing this in mind, it appears clearly that a loss of mobility at any given point in the body, is a hint as to how this loss as occurred. One way or the other, probably through the nervous system, the conjonctive tissue is constantly moving, correlatively to cranio-sacral rhythm.

Through direct connections and common bone attachment, the meninges and the extradural fascia are connected and interdependent as far as  mobility is concerned. Consequently, the diagnostic and prognostic data to be obtained through examination of the fascial mobility or lack of it, can only be limited by the examiner's palpation skills and anatomical knowledge. Attention must be focused on the quantity, the amplitude, the symmetry and the quality of the cranio-sacral mobility, and its repercussion throughout the body."
Upledger.



>> Contradictions in the osteopathic theory on PRM

- The C.R.L. production by choroid plexus occurs during the cardiac systole. If the cranial rhythm was linked to the C.R.L. production, a rate similar to the cardiac rhythm's periodicity would be observed.

- The expulsion power is not sufficient to bring the C.R.L. to the nerve ends (1,5 cm Hg at capillary level), or simply to move the sacrum from afar.
·         The purely hydraulic mechanism is inconsistent with the lesions bringing about a flexion movement of the sacrum when a cranial extension occurs.

Sacrum : sacrum
Occiput : occiput

Diagram12 - In the framework of a hydraulic theory or Dura-Mater transmission mechanics, how could some patients exhibit at the same time a flexion of the sacrum and an extension of the occiput ?
Diagram adapted from Upledger (6).

Current theories regarding these various hemodynamic aspects do not provide satisfactory answers to the questions about the mechanics of the circulation of fluids (lymph, venous blood) back to the heart. The following articles will explain why the venous blood mass is 8 times superior to the arterial volume, which is not in sync with the current theories. They will put forward the theory of Permanent Muscle Motility and the implementation of new osteopathic techniques as well as define the position and role of acupuncture in the workings of the cranio-sacral and myofascial system.





Bibliography

(1)   Biomécanique des fluides et des tissus, Michel Y. Jaffrin & Francis Goubel, Masson ed, Paris 1998
(2)   Précis de physiologie, H. Hermann & J.F. Cier, Masson ed, Paris 1976
(3)   Physiologie Humaine, A. Vander & J. Sherman & D. Luciano, R. Brière-Chenelière/Mc Graw-Hill third edition 1995
(4)   Anatomie médicale, Keith Moore & Arthur F. Dalley, De Boeck University 2001
(5)   Les feuillets d'anatomie, Brizon & J. Castaing, Maloine ed, Paris 1953
(6)   Thérapie crânio-sacrée, J. E. Upledger, I.P.C.O. ed, Paris 1983



Hervé JULIEN / Jean Louis GAUDRON
Copyright.    C2004



Translated from French by Valérie GENTA